The present invention relates electrical-energy meters, also referred to as xe2x80x9cwatt-hour metersxe2x80x9d or xe2x80x9cpower meters,xe2x80x9d for measuring consumption of electrical power. More particularly, the invention relates to a cover system for an electrical-energy meter, and to a process for manufacturing the cover system.
Electrical-energy meters are often installed in outside locations, and are thus equipped with covers to protect the various internal components of the meter from physical impacts, tampering, exposure to contaminates and adverse weather conditions, etc.
Exposure to direct sunlight can substantially raise the operating temperature of an electrical-energy meter. Electrical-energy meters of the solid-state type are particularly susceptible to elevated operating temperatures. In particular, relatively high operating temperatures are believed to decrease the reliability and the useful life of the electronic components of solid-state meters.
Electrical-energy meters of the electro-mechanical type are generally less susceptible to the effects of direct sunlight than solid-state meters. Electro-mechanical meters are usually equipped with a substantially transparent cover formed from glass. The use of a transparent cover facilitates visual access to the internal components of the meter. This feature is necessary to permit utility-company personnel to periodically read the meter, i.e., to view the nameplate and the display (readout) of the meter and thereby ascertain the amount of power consumed by the user subsequent to the prior meter reading.
Electrical-energy meters of the solid-state type are usually equipped with one or more features that protect the meter from the potentially harmful effects of direct sunlight. For example, the outer casing of solid-state meters is sometimes lined with a reflective or light-colored film that reflects or inhibits the transmission of sunlight. The film usually has a cut-out formed therein to facilitate visual access to the meter""s nameplate and display. Lining the outer cover with a reflective or light-colored film can substantially increase the overall cost of the meter. Moreover, reflective or light-colored films do not always provide adequate protection against elevated operating temperatures caused by exposure to sunlight (this phenomenon is typically referred to as xe2x80x9csolar heat gainxe2x80x9d).
Alternatively, the outer cover may be formed from an opaque material that substantially blocks the passage of all sunlight through the cover. This approach generally provides greater protection from solar heat gain than the use of reflective or light-colored films.
Covers formed from opaque materials are usually equipped with a transparent window to facilitate visual access to the nameplate and readout of the corresponding electrical-power meter. The window is typically accommodated in a cutout formed in the cover. The window is usually fixed to the cover by conventional bonding techniques such as adhesive or ultrasonic welding. The need to fix the window to the cover in a separate production step adds to the overall time and cost of producing the electrical-power meter. The specialized equipment needed to perform these production steps also adds to the overall production cost.
Covers for electrical-power meters are often required to meet one or more standards for physical-impact resistance, e.g., Underwrites Laboratories standard UL 916. Meeting these requirements generally requires a strong bond between the window and the cover. The required degree of bond strength can be difficult to achieve using conventional bonding techniques. Moreover, a hermetic (leak-proof) seal is typically required between the window and the cover to protect the internal components of the meter from water and other contaminates. Hermetic sealing between the cover and the window can be difficult to achieve on a consistent basis using conventional bonding techniques.
Conventional bonding techniques such a ultrasonic welding are usually compatible with substantially flat windows only. Hence, design features that require the use of, for example, a curved window, cannot be readily incorporated into electrical-energy meters having covers formed using ultrasonic welding.
Consequently, a need exists for a cover system for an electrical-energy meter that substantially protects the meter from solar heat gain without adding substantially to the production time and cost of the meter, and without detracting substantially from the resistance of the cover to physical impacts or contaminates. A cover system that can accommodate windows other than substantially flat windows is also desirable.
A preferred process comprises providing a pre-formed, substantially transparent window for a cover of an electrical-energy meter, and molding the cover from a molten resin that, when solidified, is substantially opaque. Molding the cover from a molten resin comprises causing a portion of the molten resin to contact a periphery of the window and allowing the portion of the molten resin to cool and thereby solidify so that the portion of the molten resin, upon solidifying, is molded over the periphery of the window and thereby seals and secures the window to the cover.
Another preferred process comprises placing a pre-formed, substantially transparent window for a cover of an electrical-energy meter in a mold, and clamping a portion of the window between a first and a second surface of the mold so that a periphery of the window is positioned within a cavity defined at least in part by the mold and the periphery of the window. The presently-preferred process also comprises introducing molten resin into the cavity so that the periphery of the mold is substantially immersed in the molten resin, and permitting the molten resin to cool and solidify so that a portion of the molten resin, upon solidifying, is molded around the periphery of the window and thereby seals and secures the window to the cover.
Another preferred process comprises clamping a window for a cover of an electrical-energy meter in a mold so that the window and the mold form a cavity and a portion of the window is positioned within the cavity, and molding a portion of the cover over the portion of the window positioned within the cavity.
A preferred embodiment of an electrical-energy meter comprises a base adapted to be mounted on a supporting surface. The electrical-energy meter also comprises a current sensor assembly comprising a plurality of contact blades extending through the base and adapted to electrically contact a conductor of electrical energy, and a current transformer mechanically coupled to the base and electrically coupled to the contact blades. The current transformer is adapted to produce an electrical output proportional to an electrical current in the conductor of electrical energy.
The electrical-energy meter further comprises a circuit-board assembly comprising a main circuit board electrically coupled to the current transformer and the contact blades. The circuit-board assembly is adapted to calculate a cumulative amount of electrical energy passing through the conductor of electrical energy based on the electrical output of the current transformer and a voltage of the conductor of electrical energy. The electrical-energy meter also comprises a cover system mounted on the base and comprising a substantially transparent window and a cover mechanically coupled to the base. A portion of the cover is molded over a portion of the window.
A preferred embodiment of a cover system for an electrical-energy meter comprises a window formed from a substantially transparent material. The cover system also comprises a substantially cup-shaped cover comprising a circumferentially-extending side portion, a rim portion unitarily formed with a first end of the side portion and adapted to mate with a base of the electrical-power meter, and a lip extending from a second end of the side portion. At least a portion of the lip is molded over a peripheral portion of the window.
Another preferred embodiment of a cover system for an electrical-energy meter comprises a substantially transparent window. The cover system also comprises a substantially cup-shaped cover comprising a circumferentially-extending side portion, a rim portion unitarily formed with a first end of the side portion and adapted to mate with a base of the electrical-power meter, and a face portion adjoining a second end of the side portion. The face portion has a cutout formed therein and adapted to receive the window, and at least a portion of the lip is molded over a peripheral portion of the window.